A 1.00 L buffer solution is prepared containing 0.150 M and 0.150 M at 25 °C
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A 1.00 L buffer solution is prepared containing 0.150 M H2PO4− and 0.150 M HPO42− at 25 °C. The second dissociation constant of phosphoric acid has pKa=7.21. The buffer will be used in an experiment that requires the pH to remain within ±0.50 pH units of its initial value after the addition of a strong monoprotic acid (HCl).
(a) Calculate the initial pH of the buffer.
(b) Derive the allowable numerical range for the ratio [HPO42−]/[H2PO4−] that keeps the pH within the required limits.
(c) Determine the maximum number of moles of HCl that can be added without exceeding the pH tolerance.
(d) Calculate the corresponding maximum volume of 2.00 M HCl that could be safely introduced into the buffer.